1. Field of the Invention
This invention relates to a magnetic recording medium wind-up method wherein a long strip-like magnetic recording medium is wound up into a coil around a core.
2. Description of the Prior Art
In general, when magnetic tapes or the like are manufactured, a magnetic layer and, when necessary, a backing layer are overlaid on a flexible plastic film 10 base, which has a wide width and which is fed from a film base roll, and are then dried in order to form a long strip-like magnetic recording medium having a wide width. Thereafter, at least the surface of the magnetic layer is calendered and made very smooth, and the long strip-like magnetic recording medium with the wide width is slit into long strip-like magnetic recording media having desired narrow widths. After the magnetic layer is overlaid on the flexible plastic film base and dried, the resulting long strip-like magnetic recording medium with the wide width is wound up around a core. Alternatively, after the long strip-like wide-width magnetic recording medium is slit into long strip-like magnetic recording media having desired narrow widths, each of the long strip-like narrow-width magnetic recording media is wound up around a core. In general, the long strip-like wide-width magnetic recording medium or the long strip-like narrow-width magnetic recording media are not cut into short lengths, but are processed with a length approximately equal to the length of the flexible plastic film base which was wound up around the film base feed roll, until they are wound up into final products such as magnetic tape cassettes. Therefore, the wind-up operation is carried out for long magnetic recording media.
In cases where the magnetic recording medium which is to be wound up around a core is long, when the magnetic recording medium is being wound up into a coil around the core, the position of loops of the magnetic recording medium can easily deviate so that the shape of the coil resembles a bamboo shoot along the axial direction of the core. In order to eliminate this problem, long magnetic recording media have heretofore been wound up while being pressed toward the core by a press roll or the like.
However, when a magnetic recording medium is moved quickly in the course of being wound up, the amount of air trapped by the moving magnetic recording medium in the space between the loops of the magnetic recording medium in the coil increases. The entrapped air causes the position of the loops of the magnetic recording medium in the coil to deviate along the axial direction of the core. Also, in cases where the coating, drying, calendering, and wind-up processes are carried out continuously in an on-line mode, or in cases where the coating, drying, calendering, slitting, and wind-up processes are carried out continuously in an on-line mode, the problem with regard to the deviation of the position of the loops of the magnetic recording medium occurs easily. This is because the .mu. value of the magnetic recording medium decreases and the magnetic recording medium slips more easily than when a first wind-up process is carried out after the coating and drying processes and a second wind-up process is carried out after the calendering and slitting processes.
In order to prevent the deviation of the loops of the magnetic recording medium in the coil along the axial direction of the core from being caused by an increase in the speed at which the magnetic recording medium moves during the wind-up process, or by a decrease in the .mu. value of the magnetic recording medium, it has been suggested that the pressing force applied to the wound-up portion of the magnetic recording medium be increased while it is being wound up. However, if the pressing force applied to the wound-up portion of the magnetic recording medium is increased while it is being wound up, the inner part of the coil, into which the magnetic recording medium has been wound up, will deform due to unevenness of the winding surface and/or due to overly tight winding. Therefore, the resulting coil of the magnetic recording medium will be of poor quality. If the pressing force applied to the wound-up portion of the magnetic recording medium during the wind-up operation is decreased until the inner part of the coil of the magnetic recording medium does not deform, the outer loops in the coil into which the magnetic recording medium is being wound become slack. Therefore, the loops of the magnetic recording medium in the coil deviate easily, and the coil takes on a shape resembling a bamboo shoot while the magnetic recording medium is being wound up or while the wind-up operation is being slowed down.